Internal-combustion engines – Free piston – Single chamber; one piston
Reexamination Certificate
2000-10-06
2003-03-04
Mancene, Gene (Department: 3747)
Internal-combustion engines
Free piston
Single chamber; one piston
Reexamination Certificate
active
06526926
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an internal combustion-engined tool, in particular, a setting tool for driving in fastening elements and having a drive piston, and a combustion chamber separated by a separation plate with a plurality of through-opening into a fore-chamber section and a main chamber section which adjoins the piston. The present invention further relates to a method of driving the piston and including igniting a combustible gas mixture in the fore-chamber section and producing gas jets which enter the main chamber section through the through-opening of the separation plate.
2. Description of the Prior Act
In the tools described above, the main chamber section adjoins the piston, and the fore-chamber section includes an ignition device for igniting, e.g., an air-fuel gas mixture, whereby gas jets are produced which enter the main chamber section.
The combustion of the air-fuel gas mixture is started in the fore-chamber section with an electrical spark produced by an ignition device. A produced flame front spreads slowly from the center of the fore-chamber section radially outwardly over the volume of the fore-chamber section. The flame front pushes the non-consumed air-fuel gas mixture ahead of itself. The non-consumed air-fuel gas mixture penetrates through the openings in the separation plate into the main chamber section(s), creating there turbulence and a pre-compression. When the flame front reaches the through-openings in the separation plate, the flame enters the main chamber section through the comparative narrow through-openings of the separation plate in accelerated fashion likewise in form of jets, flame jets, creating in the main chamber section further turbulence. The intermixed, turbulent air-fuel gas mixture in the main chamber section is ignited over the entire surface of the flame jets. It burns with a high speed which results in a high efficiency of the combustion as the cooling losses remain small.
In conventional tool, the separation plate has only one row of openings through which the flame can penetrate into the main combustion chamber. The row of openings usually is spaced by a relatively large distance from the ignition device in order to create pre-compression and a sufficient turbulence in the main chamber section. The openings are arranged in a circle concentric with the circular separation plate and the ignition point.
The velocity of the flame front in the fore-chamber section of a conventional tool, because of the laminar flame front, is very low. This results in the following drawbacks:
Because the flame front is laminar and has a low velocity, the time period between the generation of ignition sparks in the fore-chamber section and the start of combustion in the main chamber section is relatively long. This results in relatively high cooling losses, which reduces efficiency.
Because of a slow combustion of the air-fuel gas mixture in the combustion chamber, the pressure in the main chamber section is built up prematurely, resulting in early movement of the piston. To prevent the early movement of the piston, means for retaining the piston need be provided.
Because the through-openings are located far away from the ignition center, a larger portion of the air-fuel gas mixture, which is located in the fore-chamber section, burns out before the flame reaches the openings and ignite the mixture in the main chamber section. Therefore, the largest portion of the combustion of the air-fuel gas mixture in the fore-chamber section does not contribute to energy output and can be considered as a loss or waste.
Accordingly, an object of the present invention is to provide a internal combustion-engined tool of the type described above characterized by a high operational speed and a high efficiency.
Another object of the present invention is to provide a method of driving a piston of an internal combustion-engined tool of the type described above which would insure a high-speed operation of the tool.
SUMMARY OF THE INVENTION
These and other objects of the present invention, which will become apparent hereinafter, are achieved by generating gas jets with a predetermined energy by combustion, in the fore-chamber section, at least approximately a volume of a combustible mixture corresponding to the predetermined energy of the gas jets.
In this case, the volume of the combustible mixture, necessary for obtaining gas jets with the predetermined energy, is not combusted in the fore-chamber section in order to immediately produce the gas jets. Therefore, the main chamber section can be ignited relatively early, which increases the operational speed of the tool. Further, because of a relatively small volume of the combustible mixture in the fore-chamber section, the effectiveness of the combustion process increases because for producing the gas jets, there is no need to combust an excessive volume of, e.g., the air-fuel gas mixture. As a combustible mixture, also, oxygen-fuel gas mixture or any other suitable gas mixture can be used.
In accordance with advantageous embodiment of the present invention, the volume of the combustible mixture to be combusted in the fore-chamber section, i.e., the volume necessary for producing the gas jets having a predetermined energy, is determined by the radial distance of the through-openings of the separation plate from the ignition location. At that, the through-openings can be arranged as a row of through-openings located next to each other or can form a circle concentric with the ignition point.
After the ignition of the combustible mixture, a flame front is formed in the fore-chamber section in per se known manner which spreads rather slowly away from the ignition location. After a short period of time, the flame front reaches the openings in the separation plate as the distance of the openings from the ignition point was selected based on only the reduced amount of the combustible mixture which has to be combusted in the fore-chamber section in order to produce, in the main chamber section, the gas jets with a predetermined energy. Therefore, the mixture in the main chamber section is ignited very shortly after the ignition takes place in the fore-chamber section. This substantially reduces the operational cycle of the tool. Despite this, the gas or flame jets in the main chamber section have the necessary predetermined energy to provide, e.g., for a required good turbulence of the combustible mixture in the main chamber section to insure an explosion-like combustion of the combustible mixture in the main chamber section.
In order to increase the turbulence in the main chamber section even more, the arrangement of the through-openings in the separation plate can be so selected that the gas and/or flame jets, which pass through the through-openings, has a direction component extending tangentially to the row of the through-openings.
According to a further particularly advantageous embodiment of the present invention, the combustible gas mixture is fed back from the main chamber section into the fore-chamber section through further through-openings, which sometime are called backstreaming openings, which are provided in a region of the fore-chamber section where the combustible mixture in the fore-chamber section has not yet been combusted after start of the ignition in the main chamber section. This substantially increases the efficiency of the entire combustion process in the combustion chamber.
When the flame jets penetrate into the main chamber section through the first row or set of through-openings in the separation plate, the turbulent combustion, which takes place in the main chamber-section, pushes the non-consumed combustible mixture back into the fore-chamber section through the through-openings in the separation plate which are spaced further away from the ignition point than the through-openings through which flame penetrates into the main chamber section. The gas mixture, which is located further away from the ignition point, is also combusted in
Benton Jason
Hilti Aktiengesellschaft
Sidley Austin Brown & Wood LLP
LandOfFree
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